Process of injection moulding a syringe from polyethylene wax containing polypropylenne, syringe obtained thereby and particulate composition therefor

ABSTRACT

The invention provides a syringe barrel formed by injection moulding of a polypropylene composition, characterised in that said polypropylene composition contains a polyethylene wax. The invention further provides a syringe having a barrel formed by injection moulding of a polypropylene composition, characterised in that said polypropylene composition contains a polyethylene wax and a polypropylene composition suitable for such moulding.

[0001] This invention relates to improvements in and relating to theproduction of injection moulded polyolefin articles, in particularpolypropylene articles, more especially syringes.

[0002] Syringes are frequently produced by injection moulding ofpolymers. The polymers used must provide a sufficiently low frictionbetween the outer surface of the plunger and the inner surface of thesyringe barrel. In the case of polypropylene, this low friction isconventionally achieved by including a slip agent (e.g. oleamide orerucamide) in the polymer composition used for injection moulding.

[0003] However the oleamide slip agent migrates towards the surface overa period of a few weeks and causes blooming, the formation of a hazylayer which decreases the transparency of the syringe.

[0004] We have now found that by including a polyethylene wax in thepolypropylene, the slip agent can be used at concentrations at which theproblem of blooming is reduced or eliminated.

[0005] Thus viewed from one aspect the invention provides a syringebarrel formed by injection moulding of a polypropylene composition,characterised in that said polypropylene composition contains apolyethylene wax.

[0006] Viewed from a further aspect the invention provides a syringehaving a barrel formed by injection moulding of a polypropylenecomposition, characterised in that said polypropylene compositioncontains a polyethylene wax.

[0007] While the plungers in the syringes of the invention may be madeof various materials, in particular polyolefins, the syringes of theinvention preferably comprise plungers having a barrel contactingsurface of HDPE, in particular plungers formed by injection moulding ofa HDPE composition, e.g. comprising HDPE having MFR_(2.16) (190° C.) of7 to 40 and density 955 to 964 kg/m³. (MFR may be measured according toISO 1133).

[0008] The polypropylene compositions used in the production of thesyringe barrels preferably contain a slip agent, i.e. a surface frictionreducing agent. Suitable slip agents include amides of fatty acids, e.g.amides of C₁₂ to C₂₄ saturated or unsaturated fatty acids, includingsuch amides of bis or polyamines, e.g. ethylene diamine. Examples ofsuch amides include oleamide, erucamide, stearamide,ethylene-bis-stearamide, and ethylene-bis-oleamide, and mixturesthereof. Typically such slip agents will constitute 0.02 to 0.4 wt %,preferably 0.05 to 0.25 wt, more preferably 0.1 to 0.20 wt % of thepolypropylene compositions.

[0009] Oleamide is commercially available, for example as Crodamide ORfrom Croda Universal Ltd, Armoslip CP from Akzo Nobel or Atmer SA 1758or 1759 from CIBA.

[0010] The polyethylene (PE) wax used according to the present inventionwill generally be a low molecular weight ethylene homo or copolymer,e.g. having a viscosity at 140° C. of up to 100,000 mPas (e.g. 100 to100 000 mPas or 10 000 to 90 000 mpas), preferably up to 50 000 mPas,(e.g. 12 000 to 45 000 mPas) more preferably between 500 to 35000 mpas,e.g. 15 000 to 35 000 mPas or 22 000 to 28 000 mPas, particularly about25 000 mPas. Typically PE waxes with viscosity 25 000 mPas at 140° C.,e.g. produced by Ziegler catalysed polymerization, have a number averagemolecular weight (Mn) of 5 to 6 kD and an MFR_(2.16) (190° C.) of300-500 g/10 min. A viscosity of 100 000 mPas at 140° C. corresponds toMn about 8 kD and MFR_(2.16) (190° C.) about 100. In contrast,polyethylene “plastics” typically have MFR_(2.16) (190° C.) of below 80g/10 min. corresponding to Mn of about 9 kD.

[0011] PE waxes are available commercially and can be produced forexample by high pressure polymerization processes or using Zieglercatalysed polymerization. Typically Ziegler catalysis producesrelatively high density non-polar PE wax, e.g. with densities of 930 to980 kg/m³. The high pressure processes typically produce non-polar PEwaxes of lower densities, e.g. 910 to 950 kg/m³, but can also be used toproduce polar PE waxes of higher density, e.g. up to 1050 kg/m³.

[0012] While any PE wax can be used according to the invention, it ispreferred to use non-polar PE waxes of density 920 to 980 kg/M³,especially 940 to 970 kg/m³. Typically the PE wax will constitute 0.1 to10 wt %, preferably 0.2 to 4 wt %, more preferably 0.5 to 2 wt % (e.g.1.25 to 2 wt %) of the polypropylene compositions.

[0013] Examples of suitable commercially available PE waxes includeLicowax PE 190 and Licowax PE 520, available from Clariant.

[0014] The polypropylene compositions may contain other components asdesired, e.g. anti-oxidants, stabilizers, acid scavengers, clarifyingagents, coloring agents, anti-UV agents, nucleating agents, antistaticagents, etc. Typically these will be present at less than 2 wt % each,more preferably less than 0.5 wt %, relative to the total compositionweight. Examples of such components include Irganox 1010 and Irgafos 168(stabilizers from Ciba Specialty Chemicals), calcium stearate andsynthetic hydrotalcite (e.g. DHT-4A from Kyowa Chemical Industry)(acidscavengers), and 1,3:2,4-di(ethylbenzylidene)sorbitol -EBDS (e.g. NC-4from Mitsui Toatsu) and 1,3:2,4 bis(3,4-dimethylbenzylidene)sorbitol—DMDBS (e.g. Millad 3988 from MillikenChemicals)(sorbitol clarifying agents).

[0015] The polypropylene used may be any propylene homo or copolymersuitable for injection moulding, especially clarified propylene homo andcopolymers. Especially suitable are random propylene copolymers, e.g.containing up to 5% wt. comonomer, particularly 2 to 4% wt. comonomer,e.g. α-olefin comonomer, particularly ethylene. Comonomers preferably donot include but-1-ene. The polypropylene preferably has MFR_(2.16) (230°C.) of 2 to 100 g/10 min, especially 10 to 50 g/10 min, more especially15 to 30 g/10 min. Such polypropylenes are widely availablecommercially. The polypropylene preferably constitutes from 90 to 99.5wt %, more preferably 97 to 99 wt % of the polypropylene composition.

[0016] Clarified polypropylenes can be produced for example by meltblending the polypropylene with clarifying or nucleating agents, forexample sorbitol derivatives such as EDBS, MDBS(1,3:2,7-di(methyl-benzylidene)sorbitol), and DMDBS, phosphate salts(such as for example sodium 2,2′-methylenebis(4,6-di-tert.butylphenyl)phosphate), sodium benzoate, polyvinylcyclohexane, etc. Typically suchclarifying or nucleating agents can result in haze levels immediatelypost injection moulding of below 60%, more preferably below 40%, in 2 mmthick injection moulded sheets.

[0017] The polypropylene compositions as described above form a furtheraspect of the invention.

[0018] Viewed from a further aspect the invention provides a process forthe production of a syringe barrel comprising forming said barrel byinjection moulding of a PE wax-containing polypropylene composition.

[0019] Viewed from a still further aspect the invention provides aparticulate polypropylene injection moulding composition, saidcomposition containing a PE wax and preferably also a slip agent.

[0020] The syringes according to the invention will typically havevolumes, i.e. maximum injectable contents, of 0.1 to 300 mL, preferably0.2 to 150 mL. The syringe shape may be any shape achievable byinjection moulding and may be sold empty or pre-filled, e.g. withinjectable liquids such as pharmaceuticals or contrast agents.

[0021] The syringe barrels of the invention will generally becylindrical with an opening at one end for introduction of the plungerand with an opening or an openable vent at the other end through whichthe syringe contents may be expelled.

[0022] Injection moulding may be effected using equipment and conditionsconventional for injection moulding of polypropylene.

[0023] The invention also extends to other transparent injection mouldedpolypropylene articles having friction surfaces, i.e.,surfaces overwhich in use a further polymer article is intended to slide.

[0024] The invention will now be described further with reference to thefollowing Examples.

EXAMPLE 1

[0025] Injection Moulding Composition Polypropylene powder* 100 parts byweight Oleamide (Crodamide OR) 0.15 parts by weight PE-wax (LicowaxPE190 from 1.00 parts by weight Clariant) Irganox B215FF (Ciba) 0.15parts by weight DMDBS 0.2 parts by weight Synthetic hydrotalcite 0.05parts by weight

EXAMPLE 2

[0026] Injection Moulding

[0027] Syringe barrels and plungers for a 50 mL syringe were formed byinjection moulding of the composition of Example 1 and of an IDPErespectively.

EXAMPLE 3

[0028] Coefficient of Friction (COF), Haze and Visual Appearance ofInjection Moulded Articles

[0029] 2 mm thick polypropylene sheets were prepared by injectionmoulding a polypropylene composition according to the invention(substantially the same as the composition of Example 1) and acomparison composition containing no PE-wax and higher oleamide levels.The dynamic and static coefficients of friction for the sheets weredetermined and are set out in Table 1 below. TABLE 1 Oleamide PE-waxStatic Dynamic Composition % wt. % wt. COF COF Invention 0.15 1.0 0.570.34 Comparison 0.25 0.0 0.60 0.34

[0030] As can be seen, the friction characteristics were substantiallyequivalent.

[0031] Such 2 mm thick polypropylene sheets were annealed for 72 hoursat 55° C. to imitate normal “ageing” and the haze and visual appearancedetermined are set out in Table 2 below. TABLE 2 Composition Haze VisualAppearance Invention 42% bare visible surface layer Comparison 51%clearly visible greasy surface layer

1. A syringe barrel formed by injection moulding of a polypropylenecomposition, characterised in that said polypropylene compositioncontains a polyethylene wax.
 2. A barrel as claimed in claim 1 whereinsaid polyethylene wax has a viscosity at 140° C. of up to 100000 mPas.3. A barrel as claimed in claim 1 wherein said polyethylene wax has aviscosity at 140° C. of 500 to 35000 mpas.
 4. A barrel as claimed inclaim 1 wherein said polyethylene wax has a viscosity at 140° C. of 15000 to 35 000 mpas.
 5. A barrel as claimed in any one of claims 1 to 4wherein said composition contains 0.1 to 10% weight of said polyethylenewax.
 6. A barrel as claimed in any one of claims 1 to 5 wherein saidcomposition further contains a slip agent.
 7. A barrel as claimed inclaim 6 wherein said composition contains 0.02 to 0.5% weight of saidslip agent.
 8. A barrel as claimed in any one of claims 1 to 7 whereinsaid composition contains a clarified polypropylene.
 9. A barrel asclaimed in any one of claims 1 to 8 wherein said polyethylene wax isLicowax PE 190 or Lycowax PE
 250. 10. A process for the production of asyringe barrel comprising forming said barrel by injection moulding of apolypropylene composition characterised in that said polypropylenecomposition is as defined in any of claims 1 to
 9. 11. A syringe havinga barrel formed by injection moulding of a polypropylene composition,characterised in that said polypropylene composition is as defined inany of claims 1 to
 9. 12. A syringe as claimed in claim 11 having apolyolefin plunger.
 13. A syringe as claimed in claim 12 having an HDPEplunger.
 14. A syringe as claimed in any one of claims 11 to 13containing an injectable liquid.
 15. A particulate polypropyleneinjection moulding composition, characterised in that said polypropylenecomposition comprises polypropylene homopolymer or polypropylenecopolymer containing up to 5% by weight ethylene and is as defined inany of claims 1 to 9.